This invention relates generally to printing and transfer printing and more particularly to a method of, and an apparatus for applying printing onto planar and non-planar surfaces such as curved surfaces and irregularly-shaped surfaces.
A curved surface printing apparatus comprising a liquid tank for storing a liquid such as water, for example, and a printing pattern support sheet feeding device for supplying onto the surface of the liquid in this liquid tank a printing pattern support sheet so that it will float thereon, this sheet comprising a thin film of a material soluble in the liquid and a pattern to be printed which is provided on the surface of the thin film is known, one example thereof being disclosed in U.S. Pat. No. 4,010,057 to Nakanishi, patented Mar. 1, 1977.
In this known printing apparatus, when the printing pattern support sheet contacts the liquid surface, its soluble thin film partially dissolves in the liquid to a degree necessary for transfer, and the pattern to be transfer printed floats on the liquid surface together with the partially dissolved thin film. Accordingly, when the surface to be printed of an article to be printed is lowered toward this pattern on the liquid surface and submerged into the liquid, the pattern adheres to the surface to be printed because of the liquid pressure. Therefore, by raising the article out from the liquid and washing off the thin film with the liquid, the transfer printing of the pattern is completed.
An advantageous feature of this printing apparatus is that it is capable of printing any pattern onto the article surface to be printed even when this surface is a non-planar surface such as a curved surface or an irregular surface, and this apparatus is suitable for printing of surfaces such as those of plastic clock cases, television receiver cabinets, and radio receiver cabinets or cases.
In the printing apparatus of this known kind, however, the ink constituting the pattern must not be in a dry state since the pattern floating on the liquid surface in the liquid tank must adhere promptly to the article surface at the instant when the surface of the article being printed contacts the pattern. For this reason, the printing of the pattern on the thin film must be carried out by a printing press immediately before the printing pattern support sheet reaches the liquid surface. In this known printing apparatus, therefore, the pattern printed on the thin film surface can be printed only once. As a consequence, only monochrome patterns could be obtained. The reason for this is that, in multistage printing with diferent colors for the purpose of obtaining a multicolor pattern immediately prior to the floating of the sheet on the liquid surface, printing with an ink of a color of a succeeding stage cannot be carried out until the printing ink of the color of the preceding stage has dried.
Moreover, in the printing apparatus of the above stated kind, the printing press for printing the pattern on the thin film must be operated to produce the printing pattern support sheet in a quantity corresponding to the speed of the transfer printing carried out in the liquid tank. However, the printing speed of the printing press is usually far greater than that of the transfer printing, so that the printing press must be operated intermittently in such a manner that the printing pattern support sheet reaches the surface of the liquid with fresh or wet pattern which has just been printed on the film. It is apparent that such intermittent control of the printing press is difficult to attain.